This application is based on and incorporates herein by reference Japanese Patent Applications No. 2001-35888, No. 2001-35889, No. 2001-35890, No. 2001-35891 filed on Feb. 13, 2001, No. 2001-48126 filed on Feb. 23, 2001, and No. 2001-62023 filed on Mar. 6, 2001.
The present invention relates to a motor actuator including a gear drive train in combination with a planetary gear train. The present invention is preferably applied to, for example, an air conditioning system for a vehicle to open and close a damper of an air passage.
A motor actuator used in an air conditioning system for a vehicle to open and close a damper of an air passage needs low rotational speed (e.g., 5-10 rpm) and high torque (e.g., 1-2.5 Nxc2x7m). However, a DC motor used for the actuator rotates normally at 2000-5000 rpm with 0.005-0.02 Nxc2x7m. Therefore, a gear drive train having a high speed reduction ratio is inevitable for the above characteristics. A gear drive train constituting a plurality of spur gears, which are multiply combined with each other, is proposed for the motor actuator. However, that type of gear drive train is relatively expensive because a plenty of spur gears are usually used. Otherwise, a larger spur gear having more teeth needs to be used to gain a preferable speed reduction ratio. That results in an unfavorably sizeable actuator.
Besides, the above gear drive train can cause unfavorable mechanical noise and vibration due to imbalance in dynamic meshes between the gears, or the like. The noise and vibration caused by the gear drive train must be suppressed because the motor actuator applied to a damper of an air passage in an air conditioning system for a vehicle is usually mounted close to a driver""s seat.
The present invention has been made in view of the above aspects with an object to provide a compact and silent motor actuator having a gear drive train with a high speed reduction ratio. To accomplish the object, in the present invention, a planetary gear train is applied to a motor actuator.
The motor actuator includes a driving motor, and a motor gear formed on a rotary shaft of the driving motor. The motor actuator further includes an input gear which meshes with the motor gear, and a planet gear revolving around a rotation axis of the input gear when the input gear is rotated. It further includes a stationary gear which is fixed in a coaxial relation with the input gear, and meshes with the planet gear. It further includes an output gear which is different in the number of teeth from the stationary gear, is disposed rotatably in a coaxial relation with the input gear, has an output shaft, and meshes with the planet gear.
When the input gear is driven by the driving motor, the input gear is rotated at a predetermined reduced speed. At the same time, the planet gear is revolved around the rotation axis of the input gear while being rotated about its own axis. By the planetary movement of the planet gear, the output gear is rotated due to the difference in the number of teeth between the stationary gear and the output gear. Namely, when the planet gear goes around the axis once, the output gear is rotated by an angle equivalent to the difference in the number of teeth. Therefore, it is possible to rotate the output gear at a predetermined reduced speed.